Method and apparatus for recording and reproducing electronic watermark information, and recording medium

ABSTRACT

When a video signal having electronic watermark information embedded therein is recorded on a recording medium, a reference signal is inserted in the video signal at a position different from a position of embedment of the electronic watermark information. The electronic watermark information is embedded in the video signal by alteration of a luminous value of a luminance signal included in the video signal. When the video signal is reproduced from the recording medium, a luminous value of the electronic watermark information is modified based on the reference signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/139,112filed on Aug. 24, 1998, the contents of which are hereby incorporatedherein by reference in their entirety.

This application is related to application Ser. No. 09/984,029 filed onOct. 26, 2001, which, like the present application, is a continuation ofapplication Ser. No. 09/139,112.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for recordingand reproducing image data, particularly electronic watermarkinformation embedded (hidden) in video signals, which is used for thepicture recording and reproduction control or for marking the origins ofthe records, and also relates to a recording medium on which electronicwatermark information is recorded by being embedded in a video signal.

2. Description of the Prior Art

Among the several schemes proposed for embedding electronic watermarkinformation in video signals, representative one is described in thearticle entitled “Data Hiding Technique” in publication ITE TechnicalReport, Vol.21, No.31, pp.3-8. Another conventional informationembedding technique is described in publication Nikkei Electronics,No.683, pp.99-107, published in 1997. These conventional techniques areintended to embed, in a video signal, information that is different interms of statistical characteristics of image from the inherent pictureinformation carried by the video signal, and use the embeddedinformation at the time of picture reproduction for identifying theorigin of the record or producing a control signal which enables ordisable the reproducing of the video signal.

However, these publications mainly describe recording means and do notdescribe the details of means of detecting electronic watermarkinformation at the time of reproducing. Electronic watermark informationrecorded by a VCR or optical disk unit has its reproduced signal levelvaried depending on the reproduction characteristics of these apparatus.The reproduced signal waveform of the electronic watermark informationvaries also depending on the frequency characteristics of theseapparatus.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor recording and reproducing electronic watermark information and arecording medium which enable easy detection of the watermarkinformation at the time of reproducing.

Another object of the present invention is to provide a method andapparatus for recording and reproducing electronic watermark informationand a recording medium which enable easy reproduction of the embeddedelectronic watermark information even if the reproductioncharacteristics of the reproduction apparatus vary.

Still another object of the present invention is to provide a method andapparatus for recording and reproducing electronic watermark informationand a recording medium which enable easy reproduction of the electronicwatermark information even if the signal level of the watermarkinformation varies.

Still another object of the present invention is to provide a circuitarrangement which is scarcely affected by the reproduction level andfrequency characteristics of the recording apparatus in detectingelectronic watermark information included in a video signal which hasbeen recorded by the recording apparatus.

In order to achieve the above objectives, the recording medium based onthis invention is designed to record a video signal, electronicwatermark information which is embedded in the video signal and areference signal which is inserted at a position different from theposition of the watermark information in the video signal.

The inventive method of recording electronic watermark informationincludes the operational steps of embedding electronic watermarkinformation in a video signal at a minimal disturbance against the videosignal, and recording a reference signal which is inserted at a positiondifferent from the position of the watermark information in the videosignal.

The inventive method of recording and reproducing electronic watermarkinformation includes the operational steps of recording electronicwatermark information which is embedded in a video signal at a minimaldisturbance against the video signal and a reference signal which isinserted at a position different from the position of the watermarkinformation, reproducing the reference signal, and modifying thewatermark information based on the reference signal.

The inventive method of recording electronic watermark informationincludes the operational steps of calculating the visually-permissiblealteration range of luminous value of the luminance signal included in avideo signal, and altering the luminous value of the luminance signal ata predetermined position within the calculated alteration range.

The inventive method of recording electronic watermark informationincludes the operational steps of calculating the visually-permissiblealteration range of luminous value of the luminance signal included in avideo signal, and altering the luminous value of the luminance signal ata predetermined position in case the altered luminous value is withinthe calculated alteration range.

The inventive method of reproducing electronic watermark informationincludes the operational steps of detecting a reference signal fordetecting electronic watermark information from a recording medium onwhich are recorded a video signal, the watermark information which isembedded in the video signal at a minimal disturbance against the videosignal and the reference signal which is inserted at a positiondifferent from the position of the watermark information, and modifyingthe watermark information based on the reference signal.

The inventive method of reproducing electronic watermark informationincludes the operational steps of detecting a reference signal forreproducing electronic watermark information from a recording medium onwhich are recorded a video signal, the watermark information which isembedded in the video signal based on the alteration of luminous valueof the luminance signal included in the video signal and the referencesignal which is inserted at a position different from the position ofthe watermark information, and modifying the luminous value of thewatermark information based on the reference signal.

The inventive method of recording and reproducing electronic watermarkinformation includes the operational steps of recording a video signal,electronic watermark information which is embedded in the video signalat a minimal disturbance against the video signal and a reference signalwhich is inserted at a position different from the position of thewatermark information, and detecting the watermark information based onthe reference signal.

The inventive method of recording electronic watermark informationincludes the operational steps of recording a video signal, electronicwatermark information which is embedded in the video signal at a minimaldisturbance against the video signal and a reference signal which isinserted at a position different from the position of the watermarkinformation.

The inventive method of reproducing electronic watermark informationincludes the operational steps of detecting electronic watermarkinformation based on a reference signal thereby to reproduce thewatermark information from a recording medium on which are recorded avideo signal, the watermark information which is embedded in the videosignal at a minimal disturbance against the video signal and thereference signal which is inserted at a position different from theposition of the watermark information.

The inventive apparatus for recording electronic watermark informationcomprises a detection circuit which calculates the permissiblealteration range of luminous value depending on the luminous value ofthe luminance signal included in a video signal, and a watermarkinformation embedment processing circuit which embeds electronicwatermark information in the video signal by altering the luminous valueof the luminance signal at a predetermined position within thecalculated alteration range.

The inventive apparatus for recording electronic watermark informationcomprises a detection circuit which calculates the permissiblealteration range of luminous value depending on the luminous value ofthe luminance signal included in a video signal, and a watermarkinformation embedment processing circuit which embeds electronicwatermark information in the video signal by altering the luminous valueof the luminance signal at a predetermined position in case the alteredluminous value is within the calculated alteration range.

The inventive apparatus for reproducing electronic watermark informationcomprises a detection means for detecting electronic watermarkinformation based on a reference signal thereby to reproduce thewatermark information from a recording medium on which are recorded avideo signal, the watermark information which is embedded at a minimaldisturbance against the video signal and the reference signal which isinserted at a position different from the position of the watermarkinformation.

In the inventive electronic watermark information reproducing apparatus,the detection means includes a detection signal generating circuit whichgenerates a detection signal for detecting a reference signal from async signal, a sample-holding circuit which samples and holds theamplitude of the reference signal in response to the detection signal, again drift calculating circuit which calculates the gain drift based onthe amplitude of the reference signal provided by the sample-holdingcircuit, a modification circuit which modifies the luminance signalincluded in the video signal based on the calculation result provided bythe gain drift calculating circuit, and a watermark informationdetecting circuit which detects the watermark information from themodified luminance signal by using the detection signal.

In the inventive electronic watermark information reproducing apparatus,the detection means includes a detection signal generating circuit whichgenerates a detection signal for detecting a reference signal from async signal, a sample-holding circuit which samples and holds theamplitude of the reference signal in response to the detection signal, again drift calculating circuit which calculates the gain drift based onthe amplitude of the reference signal provided by the sample-holdingcircuit, a detection circuit which detects the watermark informationfrom the luminance signal included in the video signal by using thedetection signal, and a modification circuit which modifies theamplitude of the detected watermark information based on the gain driftcalculated by the gain drift calculating circuit.

The inventive apparatus for reproducing electronic watermark informationcomprises a watermark information detecting circuit which detects anelectronic watermark signal from a video signal, a reference signaldetecting circuit which detects a reference signal, and a modificationcircuit which modifies the amplitude of the watermark signal in responseto the drop in amplitude of the reference signal.

In the electronic watermark information reproduction apparatus, themodification circuit includes a gain drift calculating circuit whichcalculates the drop of gain of the reference signal.

In the electronic watermark information reproduction apparatus, thewatermark information detecting circuit includes an information positiongenerating circuit which generates a watermark information positiondetection signal based on the sync signal.

In the electronic watermark information reproduction apparatus, thereference signal detection circuit includes a reference signal positiondetecting circuit which generates a reference signal position detectionsignal based on a sync signal.

The inventive method and apparatus are designed to append preparatorilya reference signal used for the detection of electronic watermarkinformation at a specific position of a video signal and reproduce thewatermark information based on this reference signal at the time ofreproducing. The reference signal is embedded within the period ofhorizontal sync signal outside the picture display period, i.e., in theback-porch or front-porch portion, or outside the picture display area.At the time of detection, the embedded electronic watermark informationis reproduced based on the reference signal level.

Alternatively, the reference signal may be recorded within the period ofvertical sync signal. A reference timing signal is recorded at the headof the video signal so that the recording level and recording positionof the electronic watermark information are detected based on thereference signal level and reproduction timing at the time ofreproducing.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the reference signal and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on an embodiment of this invention;

FIG. 2 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on another embodiment of this invention;

FIG. 3 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention;

FIG. 4 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention;

FIG. 5 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention;

FIGS. 6A, 6B and 6C are waveform diagrams showing the first, second andthird reference signals shown in FIG. 5, the timing signal, and thesampled-and-held reference signals based on an embodiment of thisinvention;

FIG. 7 is a schematic diagram showing the reference signal and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention;

FIG. 8 is a schematic diagram showing the reference signal and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention;

FIG. 9 is a schematic diagram showing the positional relation among thereference signal shown in FIG. 7, the horizontal sync period, thepicture display area and the over-scan area;

FIG. 10 is a schematic diagram showing the positional relation among thereference signal shown in FIG. 8, the horizontal sync period, thepicture display area and the over-scan area;

FIGS. 11A and 11B are block diagrams of the electronic watermarkinformation reproduction apparatus based on an embodiment of thisinvention;

FIG. 12 is a block diagram of the electronic watermark informationreproduction apparatus based on an embodiment of this invention;

FIG. 13 is a block diagram showing an embodiment of the reference signaldetecting circuit in the electronic watermark information reproductionapparatus of this invention;

FIG. 14 is a block diagram showing another embodiment of the referencesignal detecting circuit in the electronic watermark informationreproduction apparatus of this invention;

FIG. 15 is a block diagram of the electronic watermark informationrecording apparatus based on an embodiment of this invention;

FIG. 16 is a schematic diagram showing the linear display of luminousvalues of pixels; and

FIG. 17 is a schematic diagram showing the modification of luminancebased on this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method and apparatus for recording and reproducing electronicwatermark information and the recording medium based on this inventionwill be explained with reference to the drawings.

FIG. 1 is a schematic diagram showing the reference signal and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information based on anembodiment of this invention. In the figure, numeral 1 denotes thepicture display area of a display apparatus such as a televisionreceiver, 2 is the over-scan area which is the remaining portion of thearea enclosed by the dashed lines excluding the picture display area 1,and 3 indicates the insertion position of the reference signal recordedin the over-scan area 2.

The reference signal which takes up one or more lines is inserted oradded to a video signal. The video signal, with the reference signalbeing appended thereto, is recorded on a recording medium. The referencesignal is included in the video signal so that it is located preferablyin the over-scan area, instead of the picture display area 1 in whichcase the video signal would possibly be disturbed.

FIG. 2 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on another embodiment of this invention. In thefigure, reference signals 4 and 5 are inserted or added to a videosignal so that the signals 4 and 5 are located within the upperover-scan area and lower over-scan area, respectively, and each includedin one or more lines of the video signal.

Generally, TV signals are liable to sag at the top and bottom of thescreen due to the influence of the transmission system. Specifically,when a TV signal for producing a constant luminance over the entirescreen is transmitted, it varies due to the influence of thetransmission system, resulting in a varied displayed luminance at thetop and bottom of the screen. This phenomenon is pronounced particularlyin gray colors.

This phenomenon can possibly cause the luminance of electronic watermarkinformation to vary in an asymmetric fashion. The embodiment of FIG. 2is intended to correct the luminance variation by inserting thereference signals 4 and 5 at the top and bottom of the over-scan area.In this arrangement, the detection level or luminous value of theelectronic watermark information is corrected by use of the referencesignal 4 for the top of the screen and the reference signal 5 for thebottom of the screen. Alternatively, the mean value of the upper andlower reference signals 4 and 5 may be used for the correction.Consequently, even if the luminance variation arises due to the sag, thedetection level of electronic watermark information can be corrected.

FIG. 3 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention.

In this embodiment, reference signals 6 and 7 are inserted to take uppart of the top of and part of the bottom of the over-scan area 2. Thereference signals 6 and 7 are recorded to locate at the corners of thescreen, instead of the entire lines, in which case the signals 6 and 7would distribute the video signal in its picture display period.Alternatively, a reference signal may be recorded to locate only at thetop or bottom of the over-scan area 2, instead of inserting thereference signals 6 and 7 to locate in part of the top of and part ofthe bottom of the over-scan area 2. In the case of a VCR, the head isswitched at the lower side of the tape, allowing of less space for thereference signal 7, and therefore it is advantageous to adopt thereference signal 6 in the larger area of the upper side of the tape.

The reference signals 6 and 7 added to the video signal have the peakwhite level in terms of the luminance signal. Accordingly, in case thevideo signal has its luminance varied in order to embed electronicwatermark information, the correct watermark information can be obtainedby modifying the luminance of the video signal by use of the referencesignals 6 and 7. Namely, the electronic watermark information isembedded in the video signal in terms of the varied luminance of thevideo signal, as will be explained in detail later, and the luminancelevel varied by the transmission system can be corrected by use of thereference signals 6 and 7, whereby the watermark information can bedetected easily.

FIG. 4 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention.

Shown in FIG. 4 is an example in which reference signals 8 and 9 areinserted in the over-scan area 2 immediately before and after thehorizontal sync signals. Namely, the reference signals 8 and 9 are addedto the video signal by being recorded at the beginning and end of thehorizontal sync period. Alternatively, a reference signal may beinserted only at the head or end of the horizontal sync signal forcorrecting the luminance level of the video signal, instead of addingthe reference signals 8 and 9 at the beginning and end of the horizontalsync period.

FIG. 5 is a schematic diagram showing the reference signals and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention. Inthis embodiment, a first, second and third reference signals 11,12 and13 having different luminance levels are inserted to locate in theover-scan area 2. Each of the reference signals 11,12 and 13 may be aline, instead of a block shown in FIG. 5.

FIGS. 6A, 6B and 6C are waveform diagrams of the first, second and thirdreference signals shown in FIG. 5, the timing signal, and thesampled-and-held reference signals based on an embodiment of thisinvention. FIG. 6A shows the waveform of the first, second and thirdreference signals 11,12 and 13, which are inserted between thehorizontal sync signals 15 and 16 in the over-scan area 2.

These reference signals 11,12 and 13 have different levels. For example,the first reference signal 11 has a level equal to the peak white level(IRE 100), the second reference signal 12 has a level equal to half thepeak white level (IRE 50), and the third reference signal 13 has thelevel of IRE-10.

FIG. 6B shows the waveform of the timing pulse, which provides timingsignals T1, T2 and T3 for sampling the first, second and third referencesignals 11,12 and 13, respectively. The timing signals T1, T2 and T3 aregenerated at predetermined time points by being timed to the horizontalsync signal 15. The first, second and third reference signals 11,12 and13 are sampled and held in response to the timing signals T1, T2 and T3,respectively.

The timing signals T1, T2 and T3 may be added at the head of the videosignal, in which case the signals can be used as timing signals for thedetection of electronic watermark information and can also be used as asignal for modifying the timing signals which are produced from the syncsignal.

FIG. 6C shows the waveforms of the first, second and thirdsampled-and-held reference signals 11 a,12 a and 13 a having levels A1,A2 and A3, respectively. Using these reference signals 11 a,12 a and 13a having the different levels enables the discrimination as to whetherthe variation of luminance level of the reference signals 11 a,12 a and13 a is the linear type or nonlinear type. In case the luminance variesat a constant rate irrespective of the luminance level, i.e., linearvariation, it is possible to correct the luminance of the video signalat the position where electronic watermark information is embedded byusing one of the first, second and third reference signals 11 a,12 a and13 a. In another case of a different variation rate of luminance leveldepending on the reference signal, i.e., nonlinear variation ofluminance level, a luminance variation rate for the luminance level isevaluated approximately from the levels of the first, second and thirdreference signals 11 a,12 a and 13 a and the luminance of electronicwatermark information is corrected depending on the luminance level ofthe electronic watermark information to be detected. In this manner, theluminance of electronic watermark information can be correctedaccurately.

By making the inserting positions of the first, second and thirdreference signals 11,12 and 13 synchronous with the position whereelectronic watermark information is recorded, a reference clock isproduced based on the timing signals T1, T2 and T3, and the recordingposition of the watermark information can be detected based on theclock.

Electronic watermark information is embedded in a block of 8-by-8 pixelsat a predetermined position, as described in the prior art publications.For extracting the electronic watermark information at the time ofreproducing, it is crucial to make accurate synchronization with theblock. By making the timing signals T1, T2 and T3 synchronous with theposition of embedment of electronic watermark information and recordingthe timing signals in synchronism with the 8-by-8 pixel block atrecording, it becomes possible to minimize the influence of the phasevariation of the timing signals in the transmission system.

The first, second and third reference level signals 11,12 and 13 whichhave been extract together with the watermark information are latched bythe sample-holding circuit, and used to detect the watermark informationembedded in the video signal, so that the influence of the luminancevariation by the transmission system can be corrected.

FIG. 7 is a schematic diagram showing the reference signal and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention. Inthe figure, a reference signal 21 is inserted in the horizontal blankingperiod outside the over-scan area 2, and it is considered to be locatedat the top-right position seen from the screen as shown.

FIG. 8 is a schematic diagram showing the reference signal and therecording position thereof used by the method and apparatus forrecording and reproducing electronic watermark information and therecording medium based on still another embodiment of this invention. Inthe figure, a reference signal 22 is inserted in the vertical blankingperiod outside of the over-scan area 2, and it is considered to belocated at the bottom-right position seen from the screen as shown.

FIG. 9 is a schematic diagram showing the positional relation among thereference signal shown in FIG. 7, the horizontal sync period, thepicture display area and the over-scan area. FIG. 10 is a schematicdiagram showing the positional relation among the reference signal shownin FIG. 8, the horizontal sync period, the picture display area and theover-scan area.

As shown in FIG. 9, a horizontal sync period P1 is divided into a videosignal period P2, horizontal flyback periods P3 and P4, and a syncsignal period P5. The video signal period P2 is further divided into apicture display period P6 and over-scan periods P7 and P8. The videosignal period P2 is usually set wider than the screen width P6 so thatit completely covers the screen width.

In this embodiment, the reference signal 21 is recorded to locateoutside of the picture display period P6. Indicated by 15 and 16 in FIG.9 are horizontal sync signals, and 23 is a video signal.

The reference signal 21 may be located before the video signal 23without any problem, instead of being located after the video signal 23shown in the figure.

FIG. 10 is a schematic diagram showing the positional relation among thereference signal shown in FIG. 8, the vertical sync period, the picturedisplay area and the over-scan area. As shown in FIG. 10, a verticalsync period P11 is divided into a video signal period P12, verticalflyback periods P13 and P14, and vertical sync signal period 15. Thevideo signal period P12 is further divided into a picture display periodP16 and over-scan periods P17 and P18. The video signal period P12 isusually set greater than the screen height P16 so that it completelycovers the screen height.

In this embodiment, the reference signal 22 is recorded to locateoutside of the video signal period P12. Indicated by 25 and 26 in FIG.10 are vertical sync signals, and 27 is a video signal between thevertical sync signals 25 and 26.

Next, the arrangement for reproduction based on the processing ofinformation recorded on the recording medium, with electronic watermarkinformation being embedded in it, will be explained with reference toFIGS. 11A and 11B, FIG. 12 and FIG. 13.

FIGS. 11A and 11B are block diagrams showing the recording/reproductionapparatus based on an embodiment of this invention. In FIG. 11A, arecording medium, e.g., a disk 31, has a record of a video signal,electronic watermark information embedded in the video signal and areference signal for correcting the amplitude variation at thereproduction of the watermark information. The disk 31 is driven forreproducing by the video player 32. Unless copying is inhibited by theelectronic watermark information, the video signal recorded on the disk31 can be transferred for recording to the VCR 33.

FIG. 11B shows the reproducing of the tape 34 by using the VCR 33. TheVCR 33 reproduces the record on the tape 34 only when the tape 34 is alegal duplication.

Electronic watermark information is used conceivably in two ways. One isto verify as to whether or not a disk is a legal duplication, and theother is to verify as to whether or not a tape has a legal copy ofrecord produced by a VCR.

When a disk, with electronic watermark information being recorded, isdriven for reproducing by a proper player, the player first reads thewatermark information to verify the legality of the disk and proceeds tothe reproducing operation, as will be explained in the following.

FIG. 12 is a block diagram of the reproduction apparatus based on anembodiment of this invention. The apparatus includes a disk reproducingmechanism 40, a signal processing circuit 41 which processes thereproduced signal, an output control circuit 42 which controls thetransfer of the reproduction output to the player output terminal, andan electronic watermark information detecting circuit 43.

Information recorded on the disk is reproduced by the reproducingmechanism 40 and fed to the signal processing circuit 41. If electronicwatermark information based on CGMS (Copy Generation Management System)or SCMS (Serial Copy Management System) for example is recorded on thedisk, it is read out and fed to the electronic watermark informationdetecting circuit 43. The detecting circuit 43 decodes the watermarkinformation and gives the decoded result to the output control circuit42.

The output control circuit 42 controls the delivery of the reproductionoutput in accordance with the watermark information. In case thedetecting circuit 43 has detected the copy inhibition in the watermarkinformation, the output control circuit 42 blocks the reproductionoutput. Alternatively, the detecting circuit 43 gives its copyinhibition output to the signal processing circuit 41 thereby to haltthe operation of the circuit 41.

The electronic watermark information based on CGMS is 2-bit information,and it is designed to indicate copy-enabled, one-copy-enabled, orcopy-inhibited. The electronic watermark information based on SCMS isdesigned to indicate copy-enabled or copy-inhibited.

The electronic watermark information detecting circuit 43 is involved insuch a problem that the video signal or information is distorted to haveits amplitude varied during the passage through the transmission systemand the watermark information embedded in the video signal orinformation is also varied in its amplitude and cannot be read out atthe time of reproducing.

In order to overcome this problem, the inventive method and apparatusare designed to insert a reference signal to the video signal (orinformation), as has been explained in connection with FIG. 1 throughFIG. 10. Based on this reference signal, the amplitude of the videosignal in which the watermark information is embedded is correctedthereby to improve the accuracy of detection based on the arrangementshown in FIG. 12.

The following explains with reference to FIG. 13 as an example theimprovement of detection accuracy of the detecting circuit based on themanipulation of the detecting circuit in response to a reference signalwhich is embedded in a predetermined position of the video signal.

FIG. 13 is a block diagram showing an embodiment of the reference signaldetecting circuit included in the inventive reproduction apparatus. Inthe figure, the video signal reproduced from the recording medium issupplied to the sync detection circuit 50, by which the horizontal syncsignal or vertical sync signal is detected. In response to the syncsignal detected by the sync detection circuit 50, the watermark positiondetection pulse generating circuit 51 generates a pulse which is used todetect the position of watermark information. The sync signal is alsoused by the reference signal position detection pulse generating circuit52 to generate a pulse which is used to detect the position of areference signal which is recorded by being inserted in the video signal(refer to FIG. 1 through FIG. 10 and the related explanation).

The position detection pulse generated by the reference signal positiondetection pulse generating circuit 52 is supplied to the sample-holdingcircuit 53 which samples and holds the reference signal level. Thesample-holding circuit 53 is further supplied with the video signal, andit samples and holds the amplitude of the reference signal inserted inthe video signal in response to the position detection pulse. Thesampled amplitude of the reference signal is supplied to the gain driftcalculating circuit 54.

The gain drift calculating circuit 54 is designed to calculate thevariation of reference signal amplitude, i.e., the variation of the gainof the luminance signal, caused by the transmission system, from thepredetermined amplitude of the recorded reference signal. The gain driftof luminance signal calculated by the gain drift calculating circuit 54is indicated to the gain modifying circuit 55.

The gain modifying circuit 55, which is supplied with the video signal,modifies the gain of the luminance signal of the video signal. The videosignal, with its luminance gain being modified, is supplied to theinformation detecting circuit 56, by which the electronic watermarkinformation is detected in response to the pulse supplied from thewatermark position detection pulse generating circuit 51.

In this embodiment, the gain variation of luminance signal caused by thetiming signal is calculated from the level (amplitude) of the referencesignal included in the reproduced signal, and the gain of luminancesignal of the video signal is modified based on the calculation resultfor the detection of the electronic watermark information. By correctingthe level variation of the luminance signal caused by the transmissionsystem by using the reference signal which is also distorted, it becomespossible to reproduce the watermark information by eliminating orreducing the influence of the level variation of the luminance signalcaused by the transmission system.

FIG. 14 is a block diagram showing another embodiment of the referencesignal detecting circuit included in the inventive reproductionapparatus. As shown in this figure, the output of the gain driftcalculating circuit 54 and the video signal may be supplied directly tothe watermark information detecting circuit 56 so that the watermarkinformation is detected and the luminance gain of the detectedinformation is modified based on the calculation result of the gaindrift calculating circuit 54, instead of modifying the gain of luminancesignal by the gain modifying circuit 55 in the embodiment shown in FIG.13.

In place of the circuit for detecting the position of reference signalfrom the sync signal, a timing signal detecting circuit 57 may beprovided to detect the timing signals T1, T2 and T3 of FIG. 6 so thatthe sample-holding circuit 53 samples and holds the amplitude ofreference signal by using these timing signals.

Instead of dealing with the reference signal level as explained above,the reference signal may be recorded by being inserted at apredetermined position, as shown in FIG. 6, relative to the sync signalso that the timing of reproduction of electronic watermark informationcan be modified and the watermark information can be detected moreeasily.

FIG. 15 is a block diagram of the electronic watermark informationrecording apparatus based on an embodiment of this invention. Thisembodiment is designed to embed electronic watermark information byvarying the luminance of pixels.

In FIG. 15, a video signal is fed to the input circuit 61, whichextracts the luminance signal from the video signal. The luminancesignal is supplied to the permissible alteration range calculatingcircuit 63, which calculates depending on the luminance signal thealteration range of luminance signal which does not impose a significantvisual drawback. Specifically, the calculating circuit 63 calculates thealteration range in consideration of the fact that the visual luminancedoes not much vary even for a large variation of luminance signal inpicture portions having a large luminance variation, while the luminancevariation is much visually noticeable in response to the variation ofluminance signal in picture portions having a small luminance variation.

The permissible alteration range calculating circuit 63 can beaccomplished by means of a CPU of a computer. The calculation result ofthe circuit 63 is given to the information embedment processing circuit65, which implements the process of embedding the electronic watermarkinformation in the video signal by altering the luminance of the videosignal when the luminance level is within the permissible alterationrange. The video signal, with the electronic watermark information beingembedded therein based on the alteration of luminance signal, is held inthe memory of the output circuit 67 until the end of process for oneframe of picture, and thereafter it is released from the memory.

The calculation process by the permissible alteration range calculatingcircuit 63 is implemented based on the following.

(1) At a picture portion where the variation of edge is great, thepicture does not much vary visually even for a large variation ofamplitude of the edge signal, whereas at a picture portion where theedge variation is small, the picture visually varies significantly whenthe amplitude of edge signal is altered greatly.

(2) The alteration range of picture is limited to the range in which thepicture does not vary visually, or to the range in which the visualvariation of picture does not cause the discomfort of viewers.

Based on the embedment of electronic watermark information in thismanner in terms of luminance different from the original picture, theresulting picture does not vary in a visual sense. The permissiblealteration range calculating circuit 63 memorizes the luminance beforeand after the image processing for each pixel, verifies as to whether ornot the altered luminance is within the permissible alteration range,and alters the luminance signal only if it is within the permissiblealteration range.

The information embedment processing circuit 65 initially selects pixelsto be rendered the luminance alteration among all pixels of the picture.Subsequently, the circuit 65 embeds the information by altering theluminance to specific values for the selected pixels having theluminance within the permissible alteration range. As a result, a videosignal, with the electronic watermark information being embeddedtherein, is produced, and it is released to the outside by way of theoutput circuit 67.

The circuit arrangement of FIG. 15 further includes a reference signalgenerating circuit 68. The reference signal generated by the circuit 68is supplied to the adder 69, by which the signal is added to the videosignal in which the electronic watermark information provided by theinformation embedment processing circuit 65 is embedded, and theresulting signal is recorded by way of the output circuit 67 onto therecording medium (not shown).

Next, the alteration of luminance by the information embedmentprocessing circuit 65 will be explained with reference to FIG. 16.

FIG. 16 is a schematic diagram showing along a line the luminous valuesof pixels. The luminous value of a pixel is assumed to range from 0 to255. In the figure, a plain circle on the line represents embeddedinformation “0” of a luminous value which is a multiple of 16, while afilled circle represents embedded information “1” of a luminous valuewhich is a multiple of 16 added by 8.

The basic operation of the information embedment processing circuit 65will be explained first. For obtaining the electronic watermarkinformation, it is necessary to alter the luminance of a pixel of thepicture to the closest plain circle or filled circle. Specifically,information of “0” to be embedded in a pixel is altered to a plaincircle, while information of “1” is altered to a filled circle. Forexample, for luminous value 30 of a pixel indicated by Δ in the figure,the pixel has its luminous value altered to 32 in case the informationto be embedded is “0” or altered to 24 in case the information is “1”.

Next, the usage of the permissible alteration range calculating circuit63 will be explained. In embedding the electronic watermark information,the picture occasionally varies visually due to excessive alteration ofthe luminance of pixels. For preventing this impropriety, it isnecessary to alter the pixel value within the permissible alterationrange. For example, in case a pixel Δ has luminous value 30 and has apermissible luminance alteration range of 26-33 as shown in FIG. 16, thepixel can have its luminance varied to 32 in accordance with theforegoing basic operation when the information to be embedded is “0”.Whereas, in case the information to be embedded is “1”, the targetluminance 24 is outside the permissible alteration range and thereforethe luminance value is altered to 26 that is closest to 24, oralternatively this pixel is left unchanged and other predetermined pixelis treated for luminance alteration.

The manner of extracting the electronic watermark information from thevideo signal will be explained. Initially, the pixels having variedluminous values are selected based on their predetermined positions byuse of pulses derived from the horizontal sync signal. Namely, thesepixels having varied luminous values are selected based on the same ruleas for the pixel selection by the information embedment processingcircuit 65.

Subsequently, the luminance signal of each selected pixel is taken outto determine as to whether the embedded information is “0” or “1”depending on whether the luminous value is closer to a multiple of 16 ora multiple of 16 added by 8.

Because of luminance alteration within the permissible alteration range,the information embedment processing circuit 65 will not occasionally beable to alter the luminance exactly to a multiple of 16 or a multiple of16 added by 8. Therefore, there will arise errors at a certainprobability in information extraction. This problem, however, can beovercome by embedding the same information in multiple pixels andextracting the information based on the majority decision.

In detecting the recorded electronic watermark information, it iscrucial to modify the level variation of luminance signal. On thisaccount, the inventive method and apparatus implements this modificationby using a reference signal which is recorded in advance in the videosignal, as shown in FIG. 17.

FIG. 17 is a schematic diagram showing the affair of luminancemodification based on this invention. Indicated by 70 and 71 in thefigure are positions of luminous values of the reference signal recordedin the video signal. These positions are of the first and secondluminous values of the reference signal explained in connection withFIG. 6. Another position 72 is of luminous value 128 of the electronicwatermark information resulting from the alteration of luminous value ofthe predetermined pixel.

When the amplitude of the luminance signal included in the video signaldecreases, the luminous level of the electronic watermark informationembedded in the luminance signal also falls as shown in FIG. 17, and theluminous value moves to position 72 a. Similarly, the luminous values ofthe reference signal have their positions 70 and 71 moving to positions70 a and 71 a. Based on the known luminous value 256 and the luminousvalue of reference signal, the luminous value of the position 72 a canbe altered to take the position 72.

Detection of electronic watermark information on the part ofreproduction at the same level as the part of recording willoccasionally fail due to the level variation. Whereas, the inventivemethod and apparatus are capable of correcting the luminance level onthe part of reproduction based on the reference signal recorded in thevideo signal, whereby the electronic watermark information can bedetected efficiently.

According to the present invention, even if the electronic watermarkinformation recorded in the video signal is distorted by thetransmission system, the luminance level of the watermark informationcan be corrected based on the reference signal recorded at a differentposition, and consequently the electronic watermark information can bedetected more accurately.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all aspects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changeswhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

What is claimed is:
 1. A method of recording electronic watermarkinformation comprising the steps of: embedding electronic watermarkinformation in a video signal at a minimal disturbance against saidvideo signal; and recording a reference signal which is inserted at aposition different from the position of said electronic watermarkinformation, wherein said reference signal is used to set a detectionlevel used by a detector to detect said watermark information which hasbeen embedded in said video signal.
 2. An electronic watermarkinformation recording method according to claim 1, wherein the insertionposition of said reference signal is in the over-scan area of said videosignal.
 3. An electronic watermark information recording methodaccording to claim 1, wherein the insertion position of said referencesignal is in the blanking period of a sync signal.
 4. An electronicwatermark information recording method according to claim 1, whereinsaid reference signal has an amplitude equal to the peak white level. 5.A method of recording and reproducing electronic watermark informationcomprising the steps of: embedding electronic watermark information in avideo signal at a minimal disturbance against said video signal;recording a reference signal which is inserted at a position differentfrom the position of said electronic watermark information; andreproducing said reference signal and modifying said electronicwatermark information by using said reference signal, wherein saidreference signal is used to set a detection level used by a detector todetect said watermark information which has been embedded in said videosignal.
 6. An electronic watermark information recording andreproduction method according to claim 5, wherein said electronicwatermark information is derived from the luminance signal, with theluminous value thereof being altered, at a predetermined position ofsaid video signal.
 7. An electronic watermark information recording andreproduction method according to claim 5, wherein said modification stepmodifies the luminous value of said electronic watermark informationbased on the luminous value of said reference signal.
 8. A method ofreproducing electronic watermark information comprising the steps of:detecting a reference signal for detecting electronic watermarkinformation from a recording medium on which a video signal, saidelectronic watermark information which is embedded in said video signalby the alteration of the luminous value of the luminance signal includedin said video signal and said reference signal which is inserted at aposition different from the position of embedment of said electronicwatermark information are recorded, wherein said reference signal isused to set a detection level used during said detecting step to detectsaid watermark information which has been embedded in said video signal;and modifying the luminous value of said electronic watermarkinformation based on said reference signal.
 9. An apparatus forreproducing electronic watermark information comprising: an electronicwatermark information detecting circuit which detects electronicwatermark information from a video signal; a reference signal detectingcircuit which detects a reference signal; and a modification circuitwhich modifies the amplitude of said electronic watermark informationbased on the amplitude of said reference signal, wherein said referencesignal is used to set a detection level used by said electronicwatermark information detecting circuit to detect said watermarkinformation which has been embedded in said video signal.
 10. Anelectronic watermark information reproduction apparatus according toclaim 9, wherein said modification circuit includes a gain driftcalculating circuit which calculates the drop of gain of said referencesignal.
 11. An electronic watermark information reproduction apparatusaccording to claim 9, wherein said electronic watermark informationdetecting circuit includes an electronic watermark position generatingcircuit which generates an electronic watermark information positiondetection signal based on a sync signal.
 12. An electronic watermarkinformation reproduction apparatus according to claim 9, wherein saidreference signal detecting circuit includes a reference signal positiongenerating circuit which generates a reference signal position detectionsignal based on a sync signal.
 13. An electronic watermark informationreproduction apparatus according to claim 9, wherein said referencesignal detecting circuit includes a timing signal detecting circuitwhich detects a timing signal included in said video signal.